The identification of somatic stem cell populations in mammalian tissues has raised important questions about the specification, maintenance and control of differentiation of these cells during an organism's lifespan. The experiments in this application utilize a unique in vitromodel to study the interplay of genetics and microenvironment in the regulation of plasticity and commitment of tissue derived over stem cells. In specific aim 1, we use a genome based approach to determine which pathways of gene regulation are specific to hepatocytic or bile ductular differentiation of hepatic progenitor cells and which are common to both lineages. In specific aim 2, we will determine if the Wnt signaling pathway, through the action of beta-catenin, plays a role in the maintenance of the stem cell phenotype in embryonic hepatic stem cells. In specific aim 3, candidate stem cell genes derived from our microarray analysis will be evaluated for their usefulness as hepatic stem cell markers. In specific aim 4, we will use the culture conditions we have established .for clonal growth of hepatoblasts from the murine hepatic diverticulum, to carry out clonal analysis of the developmental potential of retrovirally marked hepatic precursors from wild type and gene knock out mice, both in vitro andin vivo. An understanding of the molecular mechanisms controlling the differentiation potential of hepatic stem cells may greatly increase our ability to utilize such cells in experimental therapies for the treatment of chronic liver disease